Have Frame::tree() return a reference

Source/web/EditorClientImpl.cpp

 /*
  * Copyright (C) 2006, 2007 Apple, Inc.  All rights reserved.
  * Copyright (C) 2012 Google, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 121 matching lines @@
     if (m_spellCheckThisFieldStatus == SpellCheckForcedOn)
         return true;
     return shouldSpellcheckByDefault();
 }
 
 void EditorClientImpl::toggleContinuousSpellChecking()
 {
     if (isContinuousSpellCheckingEnabled()) {
         m_spellCheckThisFieldStatus = SpellCheckForcedOff;
         if (Page* page = m_webView->page()) {
-            for (Frame* frame = page->mainFrame(); frame && frame->document(); frame = frame->tree()->traverseNext()) {
+            for (Frame* frame = page->mainFrame(); frame && frame->document(); frame = frame->tree().traverseNext()) {
                 frame->document()->markers()->removeMarkers(DocumentMarker::MisspellingMarkers());
             }
         }
     } else {
         m_spellCheckThisFieldStatus = SpellCheckForcedOn;
         if (Frame* frame = m_webView->focusedWebCoreFrame()) {
             VisibleSelection frameSelection = frame->selection().selection();
             // If a selection is in an editable element spell check its content.
             if (Element* rootEditableElement = frameSelection.rootEditableElement()) {
                 frame->editor().didBeginEditing(rootEditableElement);
@@ skipping 540 matching lines @@
 #endif
 }
 
 void EditorClientImpl::willSetInputMethodState()
 {
     if (m_webView->client())
         m_webView->client()->resetInputMethod();
 }
 
 } // namesace WebKit